Computer Science Principles V11

Clive W. Humphris

DATA/ADDRESS BUS: Microprocessor Data Bus.  

The Data Bus in this example is just eight bits wide. However, sixteen and thirty-two bits are standard in computer systems. The data bus is not really a highway where the binary digits travel along from one place to another, although it's one way of looking at it.

A Bus is a series of connections linking up all the various microprocessor data pins on the, RAM, ROM, Accumulator etc. If the microprocessor generates a code of say binary 00110110, decimal 54 this is then available at all the other connections to the data bus.

Data can be thought of as flowing into or out of the CPU depending upon whether it is Reading the code on the bus or generating it, i.e. Writing. The data bus is bi-directional, where the address bus is one-way.

As our example is eight bits wide it can only accommodate values up to decimal 255 and data values greater than 11111111 have to be sent in two or more consecutive bytes, this slows up the processing. Therefore, generally the wider the data bus the faster the computer.

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